When a task is created the process scheduler locks and loads it. This
can cause ITaskScheduler_Delete() to fail with a sharing violation if
it is called at the wrong time. Just retry a bit later when that
happens.

This fixes failures mostly in Wine but also in Windows 10 from time
to time in both task and task_scheduler.
Signed-off-by: Francois Gouget <fgouget@icodeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>